e790a4ce52
Architecture-specific documentation is being moved into Documentation/arch/ as a way of cleaning up the top-level documentation directory and making the docs hierarchy more closely match the source hierarchy. Move Documentation/arm into arch/ (along with the Chinese equvalent translations). Cc: Maxime Coquelin <mcoquelin.stm32@gmail.com> Cc: Chen-Yu Tsai <wens@csie.org> Cc: Jernej Skrabec <jernej.skrabec@gmail.com> Cc: Samuel Holland <samuel@sholland.org> Cc: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org> Cc: Alim Akhtar <alim.akhtar@samsung.com> Cc: Alex Shi <alexs@kernel.org> Cc: linux-doc@vger.kernel.org Cc: linux-arm-kernel@lists.infradead.org Cc: linux-arch@vger.kernel.org Acked-by: Alexandre TORGUE <alexandre.torgue@foss.st.com> Reviewed-by: Yanteng Si <siyanteng@loongson.cn> Signed-off-by: Jonathan Corbet <corbet@lwn.net>
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Software emulation of deprecated SWP instruction (CONFIG_SWP_EMULATE)
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ARMv6 architecture deprecates use of the SWP/SWPB instructions, and recommeds
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moving to the load-locked/store-conditional instructions LDREX and STREX.
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ARMv7 multiprocessing extensions introduce the ability to disable these
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instructions, triggering an undefined instruction exception when executed.
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Trapped instructions are emulated using an LDREX/STREX or LDREXB/STREXB
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sequence. If a memory access fault (an abort) occurs, a segmentation fault is
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signalled to the triggering process.
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/proc/cpu/swp_emulation holds some statistics/information, including the PID of
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the last process to trigger the emulation to be invocated. For example::
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Emulated SWP: 12
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Emulated SWPB: 0
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Aborted SWP{B}: 1
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Last process: 314
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NOTE:
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when accessing uncached shared regions, LDREX/STREX rely on an external
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transaction monitoring block called a global monitor to maintain update
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atomicity. If your system does not implement a global monitor, this option can
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cause programs that perform SWP operations to uncached memory to deadlock, as
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the STREX operation will always fail.
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